Electrolytic production of iron and iron alloys



Patented Dec. 16, 1952 UNITED STATES PATENT OFFICE 2,622,063 ELECTROLYTIC PRODUCTION OF IRON AND IRON ALLOYS Erik Gustaf Robert Angel, Stockholm, Sweden No Drawing. Application J une 25,1946, Serial No.

8 Claims.

It is already known to recover iron from hydrooxygen compounds by subjecting a suspension of such a compound in an alkaline lye of a high degree of concentration to an electrolysis process at a suitable temperature. It is also known that besides iron also certain other metals, as for instance, cadmium, may be obtained as a result of a reduction process, if the suspended body except compounds of iron contains hy droxides of the respective metals. Hither-to, however, it was considered impracticable directly to reduce anhydrous oxygen compounds of iron in the same way, and it was considered necessary, if the compounds were to be used as a raw material for such a process, to first convert them in one way or the other into the hydrated state. This, of course, means a severe drawback, since the most important and purest iron ores consist of anhydrous compounds and a conversion thereof into the hydrated state is a diiiicult and expensive procedure.

Contrary to the hitherto general opinion I have found that, under certain conditions, iron may be directly recovered as a result of an electrolysis of anhydrous :ierro-oxygen compounds. Said conditions are; A high degree oi subdivision of the anhydride, an intense agitation of the suspension during the electrolysis process, a high temperature, preferably 90-l'10' (3., and a degree of concentration of the lye which is suited to the degree of subdivision 'orrate of dissolution of the anhydride. I have also found that, should the suspended ferrous raw material contain other metals than iron or should such other metals be intentionally added thereto, preferably in the form of oxides, free from water, then some of such metals as manganese, nickel, molybdenum and tungsten, may berecovered alloyed with iron at the cathode, whereas some other metals, such as vanadium, remain in the lye as alkali salts of the ,higher valence oxygen compounds of the respective metals, such as, for instance, alkali vanadinatairom which the metals may be then recovered by well-known methods.

I have further found that the recovery of iron both from hydrous and anhydrous compounds does not take place, as hitherto taught, in such a way that the suspended particles are carried by 'cataphorisis into contact with the cathode to be there reduced, since "it has been ascertained that 'the particles'under the conditions stated do not move towards the cathode but towards the anode. on the basis of experiments I have found that, what actually happens is likely to In Sweden June 30, 1945 2 be that the suspended ferrous compounds are gradually dissolved in the lye as alkali ferrite or similar compounds and deposited on the cathode by electrolysis, that is to say, a galvanic process. The solubility of the ferro-oxygen compounds in the lye, however, is very low, amounting to 0.04% at most, and varies with varying concentration of the lye. The rate of dissolution is also comparatively low. It increases with increased degree of subdivision, with increased rate of agitation, with the concentration of the lye and the temperature. The rate of dissolution of hydrous ferro-oxygen compounds is, as a'rule, above that of the corresponding anhydrous compounds. This is due, substantially, to the fact that the compounds are produced by an hydrolysis of ferrites of sodium or by a precipitation of ferric salts with ammonia, whereby they have obtained an incomparably higher degree of dispersion than anhydrides disintegrated merely by grinding. Probably, however, the rate of dissolution even at the same degree of disintegration may be higher in respect to the hydric compounds than it is in respect to the anhydrous compounds.

The observations above referred to have two results: on the one hand, they show why prior attempts with a view to electrical recovery of iron from anhydrous compounds have given negative results and, on the other hand, they teach how to carry out such a recovery process with good results.

Owing to the low degree of solubility of the oxygen compounds in an alkaline lye the contents of iron dissolved in the electrolyte are very small. It is. thus seen that with a rate of dissolution below that of precipitation the iron contents of the electrolyte will immediately sink considerably with resulting decrease of the current eificiency. The negative result of prior experiments with anhydrous compounds may be due to the fact that under the conditions prevailing the rate of dissolution was too low with relation to the rate of precipitation, that is to say, with relation to the cathodic density of current used.

,As the rate of dissolution is substantially higher in respect to the hydrous compounds than it is in respect to the anhydrous compounds, it is, .of course, more diflic-u-lt to obtaingand maintain a high current jeiiiciency with the former compounds than with the'later. .Accordingto this invention it is possible, however, to directly recoveriron from anhydrous term-oxy en com pounds, as magnetite and hermatite concentrates,

while securing a current efficiency amounting to 30-85% as related to trivalent iron.

The most important condition for obtaining the result above set forth is that the raw material should be suficiently finely divided, since the rate of dissolution increases with increasing degree of subdivision. Thus, the particles should be of a diameter not greater than 0.05 mm. and preferably less than 0.01 mm.

In order to increase the rate of dissolution and compensate for differences in concentration of the electrolyte, and prevent baking and depositmg of particles, an intense and rational agitation is of an utmost importance. In addition to a mechanical agitation, with a view to keeping the lye with the suspended particles in circulation, it is preferred to vibrate the suspension, as for instance, by means of a supersonic wave producer.

A high temperature promotes the current efficiency, the rate of dissolution of the suspended particles increasing and the high chemical polarization at the deposition of iron at the cathode decreasing with rising temperature. A high temperature acts also to avoid too high contents of hydrogen in the deposited iron and a scaling off of the deposited iron from the cathode plates. On the other hand, the attack on the material of the cell Walls and agitators and the evaporation increase with increased temperature. It is preferred to effect the electrolysis at a temperature of 90110 0.

As an electrolyte a sodium lye containing 37-60% NaOH may be used with advantage. As far as the proper electrolysis process is concerned, it is preferred to use a low degree of concentration of NaOH, yet not less than 37%. On the other hand, however, the rate of dissolution of the suspended particles increases with increased concentration of NaOH. The rate of dissolution being a predominant factor as far as the maintenance of a high current efficiency is concerned, the concentration of the lye should be chosen in the first place while paying regard to this circumstance. Accordingly, as an example, the concentration of the lye should be chosen the more high, the larger is the size of grain of the particles. From what is stated above it is evident, however, that a maximum of current yield may be obtained by securing a high degree of subdivision of the raw material, an intense agitation and a high temperature of analysis, while at the same time keeping the concentration of NaOH as low as possible without hazard to a suificiently high rate of dissolution under the working conditions prevailing. In case of a size of grain amounting to 0.01-0.02 mm., a temperature of 100 C. and an intense agitation, a concentration of 50-52% has proved most advantageous.

As a cathode material I may preferably use sheet iron or steel which is suitably prepared so that the deposited iron may be readily removed from the plates after completed electrolysis. If the electrolytically produced iron is adapted to be melted, I may also use cathodes of electrolytic iron which in this case is melted together with the precipitated iron. The cathodic density of current should preferably be Within the limits 2-6 a./dm. The higher the rate of dissolution is the higher cathodic density of current or rate of precipitation may be used.

The anodes may be of nickel, iron plated with nickel or nickel iron alloys. Such anodes will not be affected, the primary anode reaction mere- 1y comprising a formation of oxygen. The larger portion thereof is removed in gaseous form but a minor portion is required for effecting an oxidation of trivalent iron compounds to hexavalent (ferrates) as well as for eifecting an oxidation of bivalent iron compounds to trivalent compounds, if there are such bivalent compounds present. Said secondary processes of oxidation are not desirable because they reduce the current efilciency in the cathodic reduction process. The higher the anodic density of current is, the less will be the loss of current efliciency as caused by the oxidation processes. With the use of anodes of this type, thus, the anodic density of current should be higher than the cathodic one, preferably higher than 6 a./dm.

It is to be noted, however, that also iron or steel anodes or anodes of an iron alloy may be used. The primary anodic reaction comprises in this case, in part, a dissolving of iron and certain alloy components of the anodes and, in part, the formation of oxygen. The iron dissolved at the anode will then precipitate on the cathode together with iron originating from the ferrooxygen compounds. Some of the alloy components which may be included in the anodic iron will also precipitate on the cathode. Of the oxygen formed the major portion will escape as a gas, whereas a minor portion is required for effecting secondary oxidation processes in the same way as with the use of insoluble anodes. Should it be desired that the main reaction as taking place at the anode would consist in a dissolution of the anodes, so that as large a portion as possible of the electrolytic iron produced originates from the anodes, measurements should be taken which have an activating effect, such as the use of a low anodic density of current, a high temperature and adding of chlorides. If, on the contrary, it is desired that the main reaction taking place at the anode, should consist in the formation of oxy en, so that the maior portion of electrolytic iron produced will originate from the raw material suspended, then measurements should be taken which have a passivating effect, such as the choice of a high anodic density of current and a comparatively low temperature.

As raw material I may use, for instance, concentrates of magnetite or hematite, roasted iron pyrites, magnetic pyrites or siderite, or ferro oxygen compounds free from water which are obtained as a by-product of chemical or metallurgical processes. The raw material should have a content as low as possible of such impurities as Si, S, P, Al, Ti and so on, which remain in the lye, for example silicate of alkali, sulphate, phosphate, aluminate, titanate, and so on, and which cannot with advantage be recovered in any form but cause a contamination of the electrolyte or a loss of alkali hydroxide. It is therefore preferred to start with a raw material in "a' highly enriched state.

It has proved advantageous to subject the raw material to a preliminary treatment of such a nature as to cause a deranging of the grid structure or an increase of the surface activity, as by this means the rate of dissolution may be increased and the disintegration may perhaps be facilitated. Such changes of the raw material may be effected, for instance, by a roasting or partial reduction thereof. The said last-mentioned treatment has proved specially advantageous as far as the yield of current is concerned, probably due, in part, to the fact that in this way I may obtain a great increase of the surface activity or the rate ofdissolution and, in part, to the fact that the ferro-oxygen compoundshave been reduced to a lower state. of oxidation.

According to the present invention it is possible to recover in addition to iron also certain other metals, either in metallic form or in the form of alkali salts of the higher valence oxygen compounds of such metals. This is the case, for instance, when in the electrolytic production of iron according to the method above described the suspended raw material except iron also contains other metals, or if the suspension is intentionally mixed with another finely divided raw material containing other metals than iron, especially in the form of oxide. Then certain of said metals, such as manganese, nickel,- tungsten and molybdenum, may be recovered simultaneously as the iron is recovered, on the cathode, whereas certain other metals, such as vanadium, remain in the electrolyte as alkali salts, as for instance vanadinate, from which compounds the metals or compounds of metals may be then recovered according to well-known methods. It is thus possible according to the present invention to produce alloys of iron and certain other metals. It is especially remarkable, that in this way metals, which otherwise cannot be precipitated per se from an alkaline solution, may be precipitated together with iron. In the manufacture of iron alloys the alloying substances are preferably added in the form of iron ores of the oxide form, containing the respective alloying metals. If, for instance, it is desired to produce iron containing manganese, it is thus evident that iron ore containing manganese should be added in finely divided state. It is of great importance too that a slight percentage of valuable metals, such as vanadium, in the raw material may be recovered according to the invention, even though this metal cannot be obtained in metallic form.

As a current efficiency amounting to 80-85% may be obtained at a cell voltage of 1.7-1.8 v., the consumption of energy amounts to not more than 2.9-3.25 kwh./kg. iron.

What I claim is:

1. A method of electrically producing an alloy of iron comprising forming a suspension of an anhydrous ferro-oxygen compound from the class consisting of water-free magnetite, hematite,

roasted iron pyrites, and roasted siderite of a grain size less than 0.05 mm., in an electrolyte comprising an alkali metal hydroxide solution, vibrating the suspension to promote the solution of the raw material, and adding a metal of the group consisting of manganese, nickel, molybdenum, and tungsten to the electrolyte in the form of an anhydrous ferro-oxygen compound containing the metal to be added, and subjecting the resulting fluid to electrolysis at a temperature of about 100 C. to electro-deposit an iron alloy at the cathode.

2. A method of electrically producing an alloy of iron comprising subjecting to a preliminary reduction step for increasing the surface activity and reducing the ferro-oxygen compounds to a lower valence state, a compound from the class consisting of anhydrous magnetite, hematite, iron pyrites, and siderite, forming a suspension of the resulting compounds having a grain size less than 0.05 mm., in an electrolyte comprising an alkali metal hydroxide solution, and adding a metal of the group consisting of manganese, nickel, molybdenum, and tungsten to the electrolyte in the form of an anhydrous ferro-oxygen compound containing the metal to be added,

6. and subjecting the resulting" fiuid to electrolysis at a temperature of about C. to electro-deposit an iron alloy at the cathode.

3. A method of electrically producing an alloy of iron comprising forming a suspension of an anhydrous ferro-oxygen compound in finely divided state in an electrolyte, comprising an alkali metal hydroxide solution, adding a metal of the group consisting of manganese, nickel, tungsten and molybdenum to the electrolyte in the form of an anhydrous ferro-oxygen compound containing the metal to .be added and subjecting the resulting fluid to electrolysis at a temperature of about 100 C. to electro-deposit an alloy of iron at the cathode.

4. The method according to claim 3 and in which an anhydrous oxide of the metal to be added is added to the electrolyte together with the anhydrous ferro-oxygen compound.

5. A method of electrically producing iron in a state adapted to be easily pulverized comprising forming a suspension of an anhydrous ferro-oxygen compound in finely divided state in an electrolyte of concentrated alkaline lye, intensely agitating said suspension so as to cause said compounds to gradually dissolve in the electrolyte, subjecting the resulting fluid to electrolysis at a temperature of approximately 100 C. to electro-deposit the iron at the cathode while using insoluble anodes, and loading the anodes with a higher current density than that of the cathodes.

6. A process of electrically producing iron alloyed with another metal in a stated adapted to be easily pulverized which comprises grinding an anhydrous ferro-oxygen compound together with an oxide compound of one of the metals of the group consisting of manganese, nickel, tungsten and molybdenum to a grain size less than .05 mm., forming a suspension of the ground material in an alkaline electrolyte containing at least 37 per cent of alkali hydroxide, and subjecting the suspension to electrolysis at a temperature of approximately 100 C. to electrodeposit the metals at the cathode while continuously agitating the electrolyte and its content of solid particles to bring the latter in solution at substantially the same rate as the metals are deposited on the cathode.

'7. A process of electrically producing iron alloyed with another metal in a state adapted to be easily pulverized, which comprises grinding an anhydrous iron ore containing a compound of a metal of the group consisting of manganese, nickel, tungsten and molybdenum to a grain size less than .05 mm., forming a suspension of the ground material in an alkaline electrolyte containing at least 37 per cent of alkali hydroxide, and subjecting the suspension to electrolysis at a temperature of approximately 100 C. to electrodeposit the iron and said other metal on the cathode while continuously agitating the electrolyte and its content of solid particles to bring the latter in solution at substantially the same rate as the metals are deposited on the cathode.

8. A process of electrically producing iron in a state adapted to be easily pulverized from an anhydrous ferro-oxygen compounds which comprises, partially reducing said anhydrous ferro-oxygen compound, grinding said anhydrous ferro-oxygen compound to a grain size less than .05 mm., forming a suspension of the ground material in an alkaline electrolyte containing at least 3'7 per cent of alkali hydroxide and subjecting the suspension to electrolysis at a temperature of approximately 100 C. to electrodeposit iron at the cathode while continuously agitating the electrolyte and its content of solid particles to successfully bring the latter in solution at substantially the same rate as the iron is deposited on the cathode.

ERIIi GUSTAF ROBERT ANGEL.

REFERENCES CITED The following references are of record in the file of this patent:

8 UNITED STATES PATENTS Number Number 22,312 of 1907 28,897 of 1906 159,906 545,057

Name Date Cowper-Gales Apr. 7, 1908 Bodman Apr. 14, 1908 Estelle Aug. 6, 1918 Van Es Aug. 8, 1939 Young Sept. 22, 1942 FOREIGN PATENTS Country Date Great Britain Oct. 8, 1908 Great Britain May 16, 1907 Great Britain Mar. 17, 1921 Great Britain May 8, 1942 

5. A METHOD OF ELECTRICALLY PRODUCING IRON IN A STATE ADAPTED TO BE EASILY PULVERIZED COMPRISING FORMING A SUSPENSION OF AN ANHYDROUS FERRO-OXYGEN COMPOUND IN FINELY DIVIDED STATE IN AN ELECTROLYTE OF CONCENTRATED ALKALINE LYE, INTENSELY AGITATING SAID SUSPENSION SO AS TO CAUSE SAID COMPOUNDS TO GRADUALLY DISSOLVE IN THE ELECTROLYTE, SUBJECTING THE RESULTING FLUID TO ELECTROLYSIS AT A TEMPERATURE OF APPROXIMATELY 100* C. TO ELECTRO-DEPOSIT THE IRON AT THE CATHODE WHILE USING INSOLUBLE ANODES, AND LOADING THE ANODES WITH A HIGHER CURRENT DENSITY THAN THAT OF THE CATHODES. 